//===-- Twine.h - Fast Temporary String Concatenation -----------*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_ADT_TWINE_H
#define LLVM_ADT_TWINE_H

#include "llvm/ADT/StringRef.h"
#include "llvm/Support/DataTypes.h"
#include <cassert>
#include <string>

namespace llvm {
template <typename T>
class SmallVectorImpl;
class StringRef;

/// Twine - A lightweight data structure for efficiently representing the
/// concatenation of temporary values as strings.
///
/// A Twine is a kind of rope, it represents a concatenated string using a
/// binary-tree, where the string is the preorder of the nodes. Since the
/// Twine can be efficiently rendered into a buffer when its result is used,
/// it avoids the cost of generating temporary values for intermediate string
/// results -- particularly in cases when the Twine result is never
/// required. By explicitly tracking the type of leaf nodes, we can also avoid
/// the creation of temporary strings for conversions operations (such as
/// appending an integer to a string).
///
/// A Twine is not intended for use directly and should not be stored, its
/// implementation relies on the ability to store pointers to temporary stack
/// objects which may be deallocated at the end of a statement. Twines should
/// only be used accepted as const references in arguments, when an API wishes
/// to accept possibly-concatenated strings.
///
/// Twines support a special 'null' value, which always concatenates to form
/// itself, and renders as an empty string. This can be returned from APIs to
/// effectively nullify any concatenations performed on the result.
///
/// \b Implementation \n
///
/// Given the nature of a Twine, it is not possible for the Twine's
/// concatenation method to construct interior nodes; the result must be
/// represented inside the returned value. For this reason a Twine object
/// actually holds two values, the left- and right-hand sides of a
/// concatenation. We also have nullary Twine objects, which are effectively
/// sentinel values that represent empty strings.
///
/// Thus, a Twine can effectively have zero, one, or two children. The \see
/// isNullary(), \see isUnary(), and \see isBinary() predicates exist for
/// testing the number of children.
///
/// We maintain a number of invariants on Twine objects (FIXME: Why):
///  - Nullary twines are always represented with their Kind on the left-hand
///    side, and the Empty kind on the right-hand side.
///  - Unary twines are always represented with the value on the left-hand
///    side, and the Empty kind on the right-hand side.
///  - If a Twine has another Twine as a child, that child should always be
///    binary (otherwise it could have been folded into the parent).
///
/// These invariants are check by \see isValid().
///
/// \b Efficiency Considerations \n
///
/// The Twine is designed to yield efficient and small code for common
/// situations. For this reason, the concat() method is inlined so that
/// concatenations of leaf nodes can be optimized into stores directly into a
/// single stack allocated object.
///
/// In practice, not all compilers can be trusted to optimize concat() fully,
/// so we provide two additional methods (and accompanying operator+
/// overloads) to guarantee that particularly important cases (cstring plus
/// StringRef) codegen as desired.
class Twine {
  /// NodeKind - Represent the type of an argument.
  enum NodeKind {
    /// An empty string; the result of concatenating anything with it is also
    /// empty.
    NullKind,

    /// The empty string.
    EmptyKind,

    /// A pointer to a Twine instance.
    TwineKind,

    /// A pointer to a C string instance.
    CStringKind,

    /// A pointer to an std::string instance.
    StdStringKind,

    /// A pointer to a StringRef instance.
    StringRefKind,

    /// A char value reinterpreted as a pointer, to render as a character.
    CharKind,

    /// An unsigned int value reinterpreted as a pointer, to render as an
    /// unsigned decimal integer.
    DecUIKind,

    /// An int value reinterpreted as a pointer, to render as a signed
    /// decimal integer.
    DecIKind,

    /// A pointer to an unsigned long value, to render as an unsigned decimal
    /// integer.
    DecULKind,

    /// A pointer to a long value, to render as a signed decimal integer.
    DecLKind,

    /// A pointer to an unsigned long long value, to render as an unsigned
    /// decimal integer.
    DecULLKind,

    /// A pointer to a long long value, to render as a signed decimal integer.
    DecLLKind,

    /// A pointer to a uint64_t value, to render as an unsigned hexadecimal
    /// integer.
    UHexKind
  };

  union Child {
    const Twine* twine;
    const char* cString;
    const std::string* stdString;
    const StringRef* stringRef;
    char character;
    unsigned int decUI;
    int decI;
    const unsigned long* decUL;
    const long* decL;
    const unsigned long long* decULL;
    const long long* decLL;
    const uint64_t* uHex;
  };

private:
  /// LHS - The prefix in the concatenation, which may be uninitialized for
  /// Null or Empty kinds.
  Child LHS;
  /// RHS - The suffix in the concatenation, which may be uninitialized for
  /// Null or Empty kinds.
  Child RHS;
  // enums stored as unsigned chars to save on space while some compilers
  // don't support specifying the backing type for an enum
  /// LHSKind - The NodeKind of the left hand side, \see getLHSKind().
  unsigned char LHSKind;
  /// RHSKind - The NodeKind of the left hand side, \see getLHSKind().
  unsigned char RHSKind;

private:
  /// Construct a nullary twine; the kind must be NullKind or EmptyKind.
  explicit Twine(NodeKind Kind) : LHSKind(Kind), RHSKind(EmptyKind) {
    assert(isNullary() && "Invalid kind!");
  }

  /// Construct a binary twine.
  explicit Twine(const Twine& _LHS, const Twine& _RHS)
      : LHSKind(TwineKind), RHSKind(TwineKind) {
    LHS.twine = &_LHS;
    RHS.twine = &_RHS;
    assert(isValid() && "Invalid twine!");
  }

  /// Construct a twine from explicit values.
  explicit Twine(Child _LHS, NodeKind _LHSKind, Child _RHS, NodeKind _RHSKind)
      : LHS(_LHS), RHS(_RHS), LHSKind(_LHSKind), RHSKind(_RHSKind) {
    assert(isValid() && "Invalid twine!");
  }

  /// isNull - Check for the null twine.
  bool isNull() const { return getLHSKind() == NullKind; }

  /// isEmpty - Check for the empty twine.
  bool isEmpty() const { return getLHSKind() == EmptyKind; }

  /// isNullary - Check if this is a nullary twine (null or empty).
  bool isNullary() const { return isNull() || isEmpty(); }

  /// isUnary - Check if this is a unary twine.
  bool isUnary() const { return getRHSKind() == EmptyKind && !isNullary(); }

  /// isBinary - Check if this is a binary twine.
  bool isBinary() const {
    return getLHSKind() != NullKind && getRHSKind() != EmptyKind;
  }

  /// isValid - Check if this is a valid twine (satisfying the invariants on
  /// order and number of arguments).
  bool isValid() const {
    // Nullary twines always have Empty on the RHS.
    if (isNullary() && getRHSKind() != EmptyKind)
      return false;

    // Null should never appear on the RHS.
    if (getRHSKind() == NullKind)
      return false;

    // The RHS cannot be non-empty if the LHS is empty.
    if (getRHSKind() != EmptyKind && getLHSKind() == EmptyKind)
      return false;

    // A twine child should always be binary.
    if (getLHSKind() == TwineKind && !LHS.twine->isBinary())
      return false;
    if (getRHSKind() == TwineKind && !RHS.twine->isBinary())
      return false;

    return true;
  }

  /// getLHSKind - Get the NodeKind of the left-hand side.
  NodeKind getLHSKind() const { return (NodeKind)LHSKind; }

  /// getRHSKind - Get the NodeKind of the left-hand side.
  NodeKind getRHSKind() const { return (NodeKind)RHSKind; }

  /// printOneChild - Print one child from a twine.
  void printOneChild(std::ostream& OS, Child Ptr, NodeKind Kind) const;

  /// printOneChildRepr - Print the representation of one child from a twine.
  void printOneChildRepr(std::ostream& OS, Child Ptr, NodeKind Kind) const;

public:
  /// @name Constructors
  /// @{

  /// Construct from an empty string.
  /*implicit*/ Twine() : LHSKind(EmptyKind), RHSKind(EmptyKind) {
    assert(isValid() && "Invalid twine!");
  }

  /// Construct from a C string.
  ///
  /// We take care here to optimize "" into the empty twine -- this will be
  /// optimized out for string constants. This allows Twine arguments have
  /// default "" values, without introducing unnecessary string constants.
  /*implicit*/ Twine(const char* Str) : RHSKind(EmptyKind) {
    if (Str[0] != '\0') {
      LHS.cString = Str;
      LHSKind     = CStringKind;
    } else
      LHSKind = EmptyKind;

    assert(isValid() && "Invalid twine!");
  }

  /// Construct from an std::string.
  /*implicit*/ Twine(const std::string& Str)
      : LHSKind(StdStringKind), RHSKind(EmptyKind) {
    LHS.stdString = &Str;
    assert(isValid() && "Invalid twine!");
  }

  /// Construct from a StringRef.
  /*implicit*/ Twine(const StringRef& Str)
      : LHSKind(StringRefKind), RHSKind(EmptyKind) {
    LHS.stringRef = &Str;
    assert(isValid() && "Invalid twine!");
  }

  /// Construct from a char.
  explicit Twine(char Val) : LHSKind(CharKind), RHSKind(EmptyKind) {
    LHS.character = Val;
  }

  /// Construct from a signed char.
  explicit Twine(signed char Val) : LHSKind(CharKind), RHSKind(EmptyKind) {
    LHS.character = static_cast<char>(Val);
  }

  /// Construct from an unsigned char.
  explicit Twine(unsigned char Val) : LHSKind(CharKind), RHSKind(EmptyKind) {
    LHS.character = static_cast<char>(Val);
  }

  /// Construct a twine to print \arg Val as an unsigned decimal integer.
  explicit Twine(unsigned Val) : LHSKind(DecUIKind), RHSKind(EmptyKind) {
    LHS.decUI = Val;
  }

  /// Construct a twine to print \arg Val as a signed decimal integer.
  explicit Twine(int Val) : LHSKind(DecIKind), RHSKind(EmptyKind) {
    LHS.decI = Val;
  }

  /// Construct a twine to print \arg Val as an unsigned decimal integer.
  explicit Twine(const unsigned long& Val)
      : LHSKind(DecULKind), RHSKind(EmptyKind) {
    LHS.decUL = &Val;
  }

  /// Construct a twine to print \arg Val as a signed decimal integer.
  explicit Twine(const long& Val) : LHSKind(DecLKind), RHSKind(EmptyKind) {
    LHS.decL = &Val;
  }

  /// Construct a twine to print \arg Val as an unsigned decimal integer.
  explicit Twine(const unsigned long long& Val)
      : LHSKind(DecULLKind), RHSKind(EmptyKind) {
    LHS.decULL = &Val;
  }

  /// Construct a twine to print \arg Val as a signed decimal integer.
  explicit Twine(const long long& Val)
      : LHSKind(DecLLKind), RHSKind(EmptyKind) {
    LHS.decLL = &Val;
  }

  // FIXME: Unfortunately, to make sure this is as efficient as possible we
  // need extra binary constructors from particular types. We can't rely on
  // the compiler to be smart enough to fold operator+()/concat() down to the
  // right thing. Yet.

  /// Construct as the concatenation of a C string and a StringRef.
  /*implicit*/ Twine(const char* _LHS, const StringRef& _RHS)
      : LHSKind(CStringKind), RHSKind(StringRefKind) {
    LHS.cString   = _LHS;
    RHS.stringRef = &_RHS;
    assert(isValid() && "Invalid twine!");
  }

  /// Construct as the concatenation of a StringRef and a C string.
  /*implicit*/ Twine(const StringRef& _LHS, const char* _RHS)
      : LHSKind(StringRefKind), RHSKind(CStringKind) {
    LHS.stringRef = &_LHS;
    RHS.cString   = _RHS;
    assert(isValid() && "Invalid twine!");
  }

  /// Create a 'null' string, which is an empty string that always
  /// concatenates to form another empty string.
  static Twine createNull() { return Twine(NullKind); }

  /// @}
  /// @name Numeric Conversions
  /// @{

  // Construct a twine to print \arg Val as an unsigned hexadecimal integer.
  static Twine utohexstr(const uint64_t& Val) {
    Child LHS, RHS;
    LHS.uHex  = &Val;
    RHS.twine = 0;
    return Twine(LHS, UHexKind, RHS, EmptyKind);
  }

  /// @}
  /// @name Predicate Operations
  /// @{

  /// isTriviallyEmpty - Check if this twine is trivially empty; a false
  /// return value does not necessarily mean the twine is empty.
  bool isTriviallyEmpty() const { return isNullary(); }

  /// isSingleStringRef - Return true if this twine can be dynamically
  /// accessed as a single StringRef value with getSingleStringRef().
  bool isSingleStringRef() const {
    if (getRHSKind() != EmptyKind)
      return false;

    switch (getLHSKind()) {
    case EmptyKind:
    case CStringKind:
    case StdStringKind:
    case StringRefKind:
      return true;
    default:
      return false;
    }
  }

  /// @}
  /// @name String Operations
  /// @{

  Twine concat(const Twine& Suffix) const;

  /// @}
  /// @name Output & Conversion.
  /// @{

  /// str - Return the twine contents as a std::string.
  std::string str() const;

  /// toVector - Write the concatenated string into the given SmallString or
  /// SmallVector.
  void toVector(SmallVectorImpl<char>& Out) const;

  /// getSingleStringRef - This returns the twine as a single StringRef.  This
  /// method is only valid if isSingleStringRef() is true.
  StringRef getSingleStringRef() const {
    assert(isSingleStringRef() && "This cannot be had as a single stringref!");
    switch (getLHSKind()) {
    default:
      assert(0 && "Out of sync with isSingleStringRef");
    case EmptyKind:
      return StringRef();
    case CStringKind:
      return StringRef(LHS.cString);
    case StdStringKind:
      return StringRef(*LHS.stdString);
    case StringRefKind:
      return *LHS.stringRef;
    }
  }

  /// toStringRef - This returns the twine as a single StringRef if it can be
  /// represented as such. Otherwise the twine is written into the given
  /// SmallVector and a StringRef to the SmallVector's data is returned.
  StringRef toStringRef(SmallVectorImpl<char>& Out) const;

  /// toNullTerminatedStringRef - This returns the twine as a single null
  /// terminated StringRef if it can be represented as such. Otherwise the
  /// twine is written into the given SmallVector and a StringRef to the
  /// SmallVector's data is returned.
  ///
  /// The returned StringRef's size does not include the null terminator.
  StringRef toNullTerminatedStringRef(SmallVectorImpl<char>& Out) const;

  /// print - Write the concatenated string represented by this twine to the
  /// stream \arg OS.
  void print(std::ostream& OS) const;

  /// dump - Dump the concatenated string represented by this twine to stderr.
  void dump() const;

  /// print - Write the representation of this twine to the stream \arg OS.
  void printRepr(std::ostream& OS) const;

  /// dumpRepr - Dump the representation of this twine to stderr.
  void dumpRepr() const;

  /// @}
};

/// @name Twine Inline Implementations
/// @{

inline Twine Twine::concat(const Twine& Suffix) const {
  // Concatenation with null is null.
  if (isNull() || Suffix.isNull())
    return Twine(NullKind);

  // Concatenation with empty yields the other side.
  if (isEmpty())
    return Suffix;
  if (Suffix.isEmpty())
    return *this;

  // Otherwise we need to create a new node, taking care to fold in unary
  // twines.
  Child NewLHS, NewRHS;
  NewLHS.twine        = this;
  NewRHS.twine        = &Suffix;
  NodeKind NewLHSKind = TwineKind, NewRHSKind = TwineKind;
  if (isUnary()) {
    NewLHS     = LHS;
    NewLHSKind = getLHSKind();
  }
  if (Suffix.isUnary()) {
    NewRHS     = Suffix.LHS;
    NewRHSKind = Suffix.getLHSKind();
  }

  return Twine(NewLHS, NewLHSKind, NewRHS, NewRHSKind);
}

inline Twine operator+(const Twine& LHS, const Twine& RHS) {
  return LHS.concat(RHS);
}

/// Additional overload to guarantee simplified codegen; this is equivalent to
/// concat().

inline Twine operator+(const char* LHS, const StringRef& RHS) {
  return Twine(LHS, RHS);
}

/// Additional overload to guarantee simplified codegen; this is equivalent to
/// concat().

inline Twine operator+(const StringRef& LHS, const char* RHS) {
  return Twine(LHS, RHS);
}

inline std::ostream& operator<<(std::ostream& OS, const Twine& RHS) {
  RHS.print(OS);
  return OS;
}

/// @}
} // namespace llvm

#endif
